Variable capacity vane pump

ABSTRACT

A variable capacity vane pump has a plurality of vanes radially extendably installed in their respective slots that are arranged in a circumferential direction in a rotor, a cam ring rockably provided on a supporting surface in a pump body and forming a plurality of pump chambers at an inner circumference side of the cam ring in cooperation with the rotor and the vanes, and a seal member provided at an outer circumference side of the cam ring and defining a first hydraulic pressure chamber located at a side where a pump discharge amount increases and a second hydraulic pressure chamber located at a side where the pump discharge amount decreases in a space outside the outer circumference of the cam ring. A center of the cam ring is offset to an inlet port side from a center of a driving shaft.

CROSS-REFERENCE TO RELATED APPLICATION

Cross-reference is made here to commonly assigned U.S. patentapplication Ser. No. 12/678,048, which is the U.S. national phase ofinternational PCT application PCT/JP2007/068238, filed Mar. 12, 2010.

TECHNICAL FIELD

The present invention relates to a variable capacity pump, and moreparticularly to a variable capacity vane pump for power steering.

BACKGROUND ART

A conventional variable capacity vane pump which is disclosed in aPatent Document 1 controls a pump discharge amount by rocking a camring.

Patent Document 1: Japanese Patent Application Kokai Publication No.11-93856

SUMMARY OF THE INVENTION

However, in the above conventional art technique, unlike a fixedcapacity type pump, since this pump has an inlet port and an outletport, pressure is in an unbalanced state in which a pressure of anoutlet port side is greater. This outlet port side pressure acts on arotor and a driving shaft, and bends and shifts the driving shaft to aninlet port side, then the driving shaft is offset. This shift causes adeviation of a relative position between the driving shaft and the camring. Therefore a delay of a start timing of compression occurs, andthere is a problem that causes a decrease in pump efficiency and causesoscillation.

The present invention focuses attention on this problem, and an objectof the present invention is to provide a variable capacity vane pumpthat is capable of reducing the decrease in pump efficiency and theoscillation.

In order to achieve the above object, in the present invention, avariable capacity vane pump comprises: a pump body; a driving shaftrotatably supported by the pump body; a rotor provided in the pump bodyand rotatably driven by the driving shaft; a plurality of vanes radiallyextendably installed in their respective slots that are arranged in acircumferential direction in the rotor; a cam ring rockably provided ona supporting surface in the pump body and forming a plurality of pumpchambers at an inner circumference side of the cam ring in cooperationwith the rotor and the vanes; first and second members provided at bothsides in an axial direction of the cam ring; an inlet port provided atleast one of the first and second members and opening to a section ofthe pump chamber where a volume of the pump chamber increases; an outletport provided at least one of the first and second members and openingto a section of the pump chamber where the volume of the pump chamberdecreases; and a seal member provided at an outer circumference side ofthe cam ring and defining a first hydraulic pressure chamber located ata side where a pump discharge amount increases and a second hydraulicpressure chamber located at a side where the pump discharge amountdecreases in a space outside the outer circumference of the cam ring,and a center of the cam ring is offset to an inlet port side from acenter of the driving shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view in an axial direction of a vane pumpaccording to an embodiment 1.

FIG. 2 is a sectional view in a radial direction of the vane pumpaccording to the embodiment 1 (an eccentricity amount of a cam ring is amaximum).

FIG. 3 is a sectional view in a radial direction of the vane pumpaccording to the embodiment 1 (the eccentricity amount of the cam ringis a minimum).

FIG. 4 is a sectional view of a part of the vane pump in a no-load state(in a no-pump-drive state).

FIG. 5 is a schematic diagram showing a relationship between a portreference line M1-M2 and an O_(C)-O_(R) line, of a conventional art.

FIG. 6 is a schematic diagram showing a relationship between a portreference line M1-M2 and an O_(C)-O_(R) line, of the embodiment 1 of thepresent invention.

FIG. 7 is a sectional view of the part of the vane pump according to anembodiment 1-1.

FIG. 8 is a sectional view of the part of the vane pump according to anembodiment 2.

FIG. 9 is a schematic diagram showing a relationship between a portreference line M1-M2 and an O_(C)-O_(R) line, of the embodiment 2.

FIG. 10 is a schematic diagram showing a relationship between a portreference line M1-M2 and an O_(C)-O_(R) line, before applying theembodiment 2 to the conventional art.

DETAILED DESCRIPTION

According to the present invention, it is possible to provide thevariable capacity vane pump that reduces the decrease in pump efficiencyand the oscillation which are caused by the offset-shift of the drivingshaft.

In the following, the variable capacity vane pump of the presentinvention will be explained on the basis of embodiments shown indrawings.

Embodiment 1 Structure of Vane Pump

An embodiment 1 will be explained on the basis of FIGS. 1 to 7. FIG. 1is a sectional view in an axial direction of a vane pump 1. FIGS. 2 and3 are sectional views in a radial direction of the vane pump 1. FIG. 2shows a case where a cam ring 4 is positioned at an end in the negativedirection of a y-axis (an eccentricity amount of the cam ring 4 is amaximum). FIG. 3 shows a case where the cam ring 4 is positioned at anend in the positive direction of the y-axis (the eccentricity amount ofthe cam ring 4 is a minimum).

Here, in the drawings, an axial direction of a driving shaft 2 isdefined as an x-axis, and a direction in which the driving shaft 2 isinserted into first and second housings 11, 12 is positive direction ofthe x-axis. Further, an axial direction of a spring 201 that restrains arock of the cam ring 4 is defined as the y-axis (see FIG. 2), and adirection in which the spring 201 forces the cam ring 4 is the negativedirection of the y-axis. An axis orthogonal to the x-axis and the y-axisis a z-axis, and a direction where an inlet vent “IN” is located ispositive direction of the z-axis.

The vane pump 1 has the driving shaft 2, a rotor 3, the cam ring 4, anadapter ring 5, and a pump body 10. The driving shaft 2 is connected toan engine through a pulley, and rotates integrally with the rotor 3.

A plurality of slots 31 are radially formed at the rotor 3 and arrangedaround a periphery of the rotor 3. This slot 31 is a groove formed inaxial direction, and a vane 32 is provided in each slot 31. The vane 32is inserted into the slot 31 so that the vane 32 can move or extend inradial direction. In an inner radial side end portion of each slot 31, aback-pressure chamber 33, in which a pressurized fluid is provided, isformed for forcing the vane 32 outwards in the radial direction by thepressurized fluid.

The pump body 10 is formed of a first housing 11 and a second housing 12(a second member). The first housing 11 is formed into a cup-shapehaving a bottom, which opens to the positive direction of the x-axis. Ata bottom portion 111 of the first housing 11, a disk shaped side plate 6(a first member) is installed. The adapter ring 5, the cam ring 4 andthe rotor 3 are accommodated in a pump element accommodation portion 112that is an inner circumferential portion of the first housing 11, at thepositive direction side of x-axis of the side plate 6.

The second housing 12 is in liquid-tight contact with the adapter ring5, the cam ring 4 and the rotor 3 from the positive direction side ofthe x-axis. The adapter ring 5, the cam ring 4 and the rotor 3 aresandwiched between the side plate 6 and the second housing 12, and areheld by these side plate 6 and second housing 12.

On an x-axis positive direction side surface 61 of the side plate 6 andon an x-axis negative direction side surface 120 of the second housing12, inlet ports 62, 121 and also outlet ports 63, 122 are respectivelyprovided. These inlet and outlet ports communicate with the inlet vent“IN” and an outlet vent “OUT” respectively, then supply and exhaust ofworking fluid for a pump chamber “B” that is formed between the rotor 3and the cam ring 4 are done.

The adapter ring 5 is an oval-shaped ring member that is formed into asubstantially oval whose y-axis is major (longer) axis and whose z-axisis minor axis. The adapter ring 5 is installed inside the first housing11, and the cam ring 4 is installed inside the adapter ring 5. In orderfor the adapter ring 5 not to rotate in the first housing 11 during thepump drive, the rotation of the adapter ring 5 with respect to the firsthousing 11 is restrained by a pin 40.

The cam ring 4 is a ring shaped member that is formed into asubstantially perfect circle, and its diameter is substantially equal toa diameter of an inner circumference of the minor axis of the adapterring 5. Therefore, since the cam ring 4 is installed inside theoval-shaped adapter ring 5, a hydraulic pressure chamber “A” is definedbetween the inner circumference of the adapter ring 5 and an outercircumference of the cam ring 4 in a space outside the outercircumference of the cam ring 4. The cam ring 4 can therefore rock ortilt inside the adapter ring 5 in the y-axis direction.

A seal member 50 (a first seal member) is provided at a top end portionin the positive direction of the z-axis on an adapter ring innercircumferential surface 53. On the other hand, at a bottom end portionin negative direction of the z-axis on the inner circumferential surface53, a supporting surface “N” is formed. The adapter ring 5 supports thecam ring 4 and stops a movement in the negative direction of the z-axisof the cam ring 4 by the supporting surface “N”.

On the supporting surface “N”, the pin 40 (a second seal member) isprovided. The above mentioned hydraulic pressure chamber “A” between thecam ring 4 and the adapter ring 5 is divided into two hydraulic pressurechambers by this pin 40 and the seal member 50 at the negative andpositive direction sides of the y-axis respectively, and a firsthydraulic pressure chamber A1 and a second hydraulic pressure chamber A2are defined.

Here, since the cam ring 4 rocks or tilts while rotating on thesupporting surface “N”, each capacity or volume of the first and secondhydraulic pressure chambers A1, A2 is varied. However, the supportingsurface “N” at the negative direction side of the z-axis is formed to beparallel to ξ-axis that is defined by rotating the y-axis in acounterclockwise direction with an origin point being a center. That is,the supporting surface “N” slants or slopes in the positive direction ofthe z-axis as the supporting surface “N” extends in the positivedirection of the y-axis. And then, this sloping supporting surface “N”allows the cam ring 4 easily to rock or tilt in the negative directionof the y-axis.

Since an inlet pressure is supplied into the second hydraulic pressurechamber A2, a supporting force of the cam ring 4 by a second hydraulicpressure chamber A2 internal pressure cannot be sufficiently obtained.The cam ring 4 is then likely to tilt to a second hydraulic pressurechamber A2 side (the positive direction side of the y-axis). However, bysetting a supporting position on the supporting surface “N” under a highrotation low pressure condition to be higher than that under a lowrotation high pressure condition (by setting the supporting positionunder the high rotation low pressure condition to be on an inlet port62, 121 side), the tilt of the cam ring 4 is prevented.

An outside diameter of the rotor 3 is smaller than that of a cam ringinner circumference 41 of the cam ring 4, and the rotor 3 is installedinside the cam ring 4. The rotor 3 is provided so that an outercircumference of the rotor 3 does not touch the cam ring innercircumference 41 even when the cam ring 4 rocks and a relative positionbetween the rotor 3 and the cam ring 4 changes.

In a case where the cam ring 4 rocks and is positioned at the end in thenegative direction of the y-axis inside the adapter ring 5, a distance“L” between the cam ring inner circumference 41 and the outercircumference of the rotor 3 becomes a maximum. On the other hand, in acase where the cam ring 4 is positioned at the end in the positivedirection of the y-axis inside the adapter ring 5, the distance “L”becomes a minimum.

A length in the radial direction of the vane 32 is set to be longer thanthe maximum distance “L”. Therefore, the vane 32 always touches the camring inner circumference 41 while being inserted in the slot 31irrespective of the relative position between the rotor 3 and the camring 4. By this setting, the vane 32 always receives a back pressurefrom the back-pressure chamber 33, and the vane 32 liquid-tightlytouches the cam ring inner circumference 41.

Accordingly, liquid-tight spaces between the cam ring 4 and the rotor 3are always defined by the plurality of the adjacent vanes 32, and thepump chamber “B” is formed. Under a state where a center of the cam ring4 shifts from a center of the rotor 3 by the rock of the cam ring 4(i.e. the rotor 3 and the cam ring 4 are under an eccentric position),volume of each pump chamber “B” varies by the rotation of the rotor 3.

The inlet ports 62, 121 and the outlet ports 63, 122, respectivelyprovided in the side plate 6 and the second housing 12, are formed alongthe outer circumference of the rotor 3, and the supply and exhaust ofthe working fluid are done by the volume change of the each pump chamber“B”.

At an end portion in the positive direction of the y-axis of the adapterring 5, a radial-direction penetration hole 51 is formed. Further, aplug member insertion hole 114 is formed at an end portion in thepositive direction of the y-axis of the first housing 11. Then, a plugmember 70 formed into a cup-shape having a bottom is inserted into theplug member insertion hole 114, and an inside of the pump is insulatedfrom an outside of the first and second housings 11, 12 and theliquid-tight inside of the pump is maintained.

The previously mentioned spring 201 is inserted into the plug member 70,and is secured in an inner circumference of the plug member 70 so thatthe spring 201 is extendable and contractible in the y-axis direction.More specifically, the spring 201 penetrates the radial-directionpenetration hole 51 of the adapter ring 5 and touches or contacts thecam ring 4, then forces the cam ring 4 in the negative direction of they-axis.

The spring 201 is a spring that forces the cam ring 4 in the negativedirection of the y-axis, in which an amount of the rock of the cam ring4 becomes a maximum. Further, the spring 201 is the one that stabilizesthe discharge amount (a rocking position of the cam ring 4) during apump startup in which the pressure is not steady.

In the embodiment, an opening of the radial-direction penetration hole51 of the adapter ring 5 acts as a stopper that limits the rock in thepositive direction of the y-axis of the cam ring 4. However, the plugmember 70 itself could penetrate the radial-direction penetration hole51 and protrude from the inner circumference of the adapter ring 5, andthen act as the stopper for limiting the rock in the positive directionof the y-axis of the cam ring 4.

[Supply of the Pressurized Fluid to First and Second Hydraulic PressureChambers]

A through hole 52 is provided at upper portion in the positive directionof the z-axis of the adapter ring 5, at a side of the seal member 50 inthe negative direction of the y-axis. This through hole 52 communicateswith a control valve 7 via an oil passage 113 that is provided insidethe first housing 11. In addition, the through hole 52 communicates withthe first hydraulic pressure chamber A1 formed at the negative directionside of the y-axis, then connects the first hydraulic pressure chamberA1 and the control valve 7. The oil passage 113 opens to a valveinstallation hole 115 that installs the control valve 7 therein, and acontrol pressure “Pv” is introduced into the first hydraulic pressurechamber A1 with the pumping action.

The through hole 52 provided at the adapter ring 5 is formed at a middleportion of adapter ring's width in the axis direction, so that an outercircumferential surface of the adapter ring 5 acts as a seal surface andleakage can be reduced.

The control valve 7 connects to the outlet ports 63, 122 through oilpassages 21 and 22. An orifice 8 is provided on the oil passage 22, andan outlet pressure “Pout” that is an upstream pressure of the orifice 8and a downstream pressure “Pfb” of the orifice 8 are introduced into thecontrol valve 7. Then, the control valve 7 is driven by a pressuredifference between these “Pout” and “Pfb” and a valve spring 7 a, andthe control pressure “Pv” is produced.

Thus, since the control pressure “Pv” is introduced into the firsthydraulic pressure chamber A1 and this control pressure “Pv” is producedon the basis of an inlet pressure “Pin” and the outlet pressure “Pout”,a relationship between the control pressure “Pv” and the inlet pressure“Pin” is; control pressure “Pv”≧inlet pressure “Pin”.

On the other hand, the inlet pressure “Pin” is introduced into thesecond hydraulic pressure chamber A2 through a communication path 64.This communication path 64 is an oil path which communicates with theinlet vent “IN” and with the x-axis negative direction side surface 120in the second housing 12 then connects the inlet vent “IN” and thesecond hydraulic pressure chamber A2. The communication path 64 alwaysopens to the second hydraulic pressure chamber A2 irrespective of therocking position of the cam ring 4.

Therefore, the second hydraulic pressure chamber A2 is supplied with theinlet pressure “Pin” all the time. With this, in the vane pump 1 of thepresent invention, only a fluid pressure P1 of the first hydraulicpressure chamber A1 is controlled. On the other hand, a fluid pressureP2 of the second hydraulic pressure chamber A2 is not controlled, andthe fluid pressure P2 is equal to the inlet pressure “Pin” (P2=inletpressure “Pin”) all the time. With this, pressure leakage from thesecond hydraulic pressure chamber A2 side to the inlet port 62, 121 sideis reduced, and the decrease in the pump efficiency is suppressed.

[Rocking of Cam Ring]

When a biasing force in the positive direction of the y-axis which thecam ring 4 receives from the pressure P1 of the first hydraulic pressurechamber A1 becomes greater than a biasing force in the negativedirection of the y-axis which the cam ring 4 receives from the pressureP2 of the second hydraulic pressure chamber A2 and the spring 201, thecam ring 4 rocks in the positive direction of the y-axis with the pin 40being a rotation center. A volume of a pump chamber By+ on the positivedirection side of the y-axis increases by the rock of the cam ring 4,while a volume of a pump chamber By− on the negative direction side ofthe y-axis decreases.

When the volume of the pump chamber By− on the negative direction sideof the y-axis decreases, an oil amount which is supplied from the inletports 62, 121 to the outlet ports 63, 122 in a unit time decreases, andthe outlet pressure is reduced. With this reduction, the pressure P1 ofthe first hydraulic pressure chamber A1 into which the outlet pressureis introduced is also reduced. Then when the total biasing force in thenegative direction of the y-axis becomes greater, the cam ring 4 rocksin the negative direction of the y-axis.

When both the biasing force in the positive direction of the y-axis andthe biasing force in the negative direction of the y-axis substantiallybecome equal to each other, the both forces in the y-axis direction,which act on the cam ring 4, balance out, then the cam ring 4 rests.When the outlet pressure is increased, the cam ring 4 rocks in thepositive direction of the y-axis, and a position of a center of axis ofthe cam ring 4 becomes identical with that of the rotor 3. Then volumesof both pump chambers By+, By− on the positive and negative directionsides of the y-axis become equal to each other, and the pressurerelationship is inlet pressure=outlet pressure=0.

With this, the pressure P1 of the first hydraulic pressure chamber A1also becomes 0, and the cam ring 4 is forced in the negative directionof the y-axis by the biasing force F of the spring 201. In this way, theoutlet pressure “Pout” is reset, and the eccentricity amount of the camring 4 is adjusted so that the pressure difference between the upstreamand downstream of the discharge orifice is constant.

[Deviation of Positions Between Driving Shaft Center and Cam RingCenter]

FIG. 4 is a sectional view of a part of the vane pump 1 in a no-loadstate (in a no-pump-drive state). A center of the driving shaft 2 andthe rotor 3 is defined as O_(R), a center of the cam ring 4 is definedas O_(C).

In the present embodiment, the cam ring center O_(C) in the no-loadstate is set so that the cam ring center O_(C) is positioned at theinlet port 62, 121 side (the positive direction side of the z-axis) ascompared with the center O_(R) of the driving shaft 2. The rotor 3 isforced from the negative direction side of the z-axis by the outletpressure, and the driving shaft 2 is bent and shifted in the positivedirection of the z-axis by this biasing force.

Thus, since the center O_(R) of the driving shaft 2 shifts in thepositive direction of the z-axis, the center O_(C) of the cam ring 4 ispreviously offset to the positive direction side of the z-axis ascompared with the driving shaft center O_(R). More specifically, byslanting the supporting surface “N”, a position in the z-axis directionof the cam ring 4 is set to be high. With this setting, even when thedriving shaft 2 is bent and shifted by the outlet pressure during thepump drive, a stable discharge amount can be ensured (details will beexplained later).

The cam ring inner circumference 41 and the outer circumference of therotor 3 are substantially circular. Therefore when the cam ring centerO_(C) and the driving shaft center O_(R) are identical with each other,the distance “L” between the cam ring inner circumference 41 and theouter circumference of the rotor 3 is uniformly equal throughout theircircumferences.

When the center O_(C) of the cam ring 4 shifts from the center O_(R) ofthe rotor 3 and the driving shaft 2, the distance “L” between the camring inner circumference 41 and the outer circumference of the rotor 3is not uniformly equal, and the distance “L” takes a maximum vale and aminimum value on an O_(C)-O_(R) straight line.

The vane 32 is forced outwards in the radial direction by the pressurefrom the back-pressure chamber 33, therefore when the distance “L”varies, a protrusion amount of the vane 32 also varies. Because of this,the volume of the pump chamber “B” defined by the outer circumference ofthe rotor 3 and the cam ring inner circumference 41 and the vane 32 alsovaries depending on the distance “L”.

That is to say, in a case of a position of the cam ring 4 where thedistance “L” between the cam ring inner circumference 41 and the outercircumference of the rotor 3 is large, the volume of the pump chamber“B” is also large. In a case of the position of the cam ring 4 where thedistance “L” is small, the volume of the pump chamber “B” is small.Consequently, at a point before and after the distance “L” becomes themaximum value Lmax on the O_(C)-O_(R) straight line (at the negativedirection side of the y-axis on the O_(C)-O_(R) straight line) by therotation of the rotor 3, the volume of the pump chamber “B” changes fromthe increase to the decrease. On the other hand, at a point before andafter the distance “L” becomes the minimum value Lmin on the O_(C)-O_(R)straight line (at the positive direction side of the y-axis on theO_(C)-O_(R) straight line), the volume of the pump chamber “B” changesfrom the decrease to the increase.

Since the rotor 3 rotates in the counterclockwise direction, when a vane32 a of the eleven vanes 32 crosses the O_(C)-O_(R) straight line at thenegative direction side of the y-axis, a volume of a pump chamber Ba atthe positive direction side of the z-axis from the O_(C)-O_(R) straightline increases. However, when the vane 32 is positioned exactly on theO_(C)-O_(R) straight line, the volume change becomes zero. And when thevane 32 is positioned on the negative direction side of the z-axis aftercrossing the O_(C)-O_(R) straight line, the volume changes to thedecrease.

That is, each time the vane 32 a crosses the O_(C)-O_(R) straight lineat the negative direction side of the y-axis, the volume of the pumpchamber Ba changes from the increase to the decrease. Likewise, eachtime the vane 32 a crosses the O_(C)-O_(R) straight line at the positivedirection side of the y-axis, the volume of the pump chamber Ba changesfrom the decrease to the increase. With this, each time the vane 32crosses the O_(C)-O_(R) straight line, positive and negative of thevolume change of the pump chamber “B” are switched.

[Port Reference Line]

Suction and discharge in the pump chamber “B” change between the inletports 62, 121 and the outlet ports 63, 122. Positions of the vane 32 atsuction/discharge change point are first and second reference positionsM1, M2. The first reference position M1 is positioned at the negativedirection side of the y-axis, while the second reference position M2 ispositioned at the positive direction side of the y-axis.

In the embodiment 1, a space between the adjacent vanes 32 is 1 pitch,and a position of the first reference position M1 is ahalf-pitch-advanced position from end edges 62 a, 121 a (edge portionsof rotation direction of the rotor 3) of the inlet ports 62, 121.Likewise, a position of the second reference position M2 is ahalf-pitch-advanced position from end edges 63 a, 122 a (edge portionsof rotation direction of the rotor 3) of the outlet ports 63, 122.

An M1-M2 line formed by these M1 and M2 is defined as a port referenceline M1-M2. Thus in the embodiment 1, each time the vane 32 a passesthrough this port reference line M1-M2, the suction and discharge of thepump chamber Ba are switched.

Because of this, a Z-axis positive direction side section Bz+, which islocated on the positive direction side of the z-axis (the inlet port 62,121 side) as compared with the port reference line M1-M2, is a suctionsection. A Z-axis negative direction side section Bz−, which is locatedon the negative direction side of the z-axis (the outlet port 63, 122side) as compared with the port reference line M1-M2, is a dischargesection.

Hence, in order to stabilize the discharge of the vane pump 1, it isdesirable that the O_(c)-O_(R) line on which the positive/negative ofthe volume change of the pump chamber “B” are switched and the portreference line M1-M2 on which the suction/discharge of the pump chamberB are switched should be as close as possible to each other. Inparticular, if the both lines are close to each other at the firstreference position M1 that is the switch position from the suction tothe discharge, the discharge amount is stable. Thus, it is desirablethat the O_(C)-O_(R) line and the port reference line M1-M2 should be asclose as possible to each other and also as parallel as possible to eachother.

[Relationship Between Port Reference Line and O_(C)-O_(R) Line]

FIGS. 5 and 6 are schematic diagrams showing a relationship between theport reference line M1-M2 and the O_(c)-O_(R) line.

FIG. 5 is a conventional art (positions of the center O_(C) of the camring 4 and the center O_(R) of the driving shaft 2 in the no-load state(in the no-pump-drive state) is shown). FIG. 6 is the embodiment 1 (acase where the cam ring center O_(C) is positioned at the positivedirection side of the z-axis as compared with the port reference lineM1-M2 in the no-load state is shown).

Here, in the drawings, a thick solid line is the port reference lineM1-M2, a thick alternate long and short dash line is the O_(C)-O_(R)line under a pump high pressure condition, and a thick broken line isthe O_(C)-O_(R) line under a pump low pressure condition.

The cam ring center O_(C) shifts in the y-axis direction by the rock ofthe cam ring 4. Then at the no-load and at the maximum eccentricity atwhich a speed is a low speed (see FIG. 2), the cam ring center O_(C) iswidely offset from the driving shaft center O_(R) in the negativedirection of the y-axis. On the other hand, at a high speed, theeccentricity amount of the cam ring 4 is small and an offset amount ofthe cam ring center O_(C) is also small. However, the cam ring centerO_(C) is still offset from the driving shaft center O_(R).

Here, when the pump 1 is driven and the pressure is produced in the pumpchamber “B”, the Z-axis negative direction side section Bz− becomes thehigh pressure, while the Z-axis positive direction side section Bz+becomes the low pressure, with the port reference line M1-M2 being aboundary in the pump chamber “B”, and the pressure difference thereforeoccurs.

By this pressure difference, the rotor 3 is forced in the positivedirection of the z-axis together with the driving shaft 2, and thedriving shaft 2 is elastically bent in the positive direction of thez-axis. The center O_(R) of the driving shaft 2 also shifts to thepositive direction side of the z-axis due to this elastic deformation,then the deviation between the cam ring center O_(C) and the drivingshaft center O_(R) appears. A deviation amount becomes great at the highpressure, while it becomes small at the low pressure.

As a consequence, due to the elastic deformation of the driving shaft 2by the outlet pressure, each of the O_(C)-O_(R) lines at the highpressure and at the low pressure widely slopes with respect to the portreference line M1-M2. Angles of the O_(C)-O_(R) lines at the highpressure and at the low pressure with respect to the port reference lineM1-M2, are α′, β′. α′ and β′ are both large, and thus the O_(C)-O_(R)line and the port reference line M1-M2 are positioned away from eachother at the first and second reference positions M1, M2 at which thesuction/discharge are switched, and this results in an unstabledischarge.

On the other hand, in the embodiment 1 of the present invention, the camring center O_(C) is previously offset to the positive direction side ofthe z-axis (the inlet port 62, 121 side) from the driving shaft centerO_(R). For this reason, even when the driving shaft 2 is bent by theoutlet pressure and driving shaft center O_(R) shifts to the positivedirection side of the z-axis, the O_(C)-O_(R) line does not widely slopewith respect to the port reference line M1-M2.

With this setting, an angle α defined by the O_(C)-O_(R) line and theport reference line M1-M2 during the pump drive becomes smaller than theα′ of the conventional art (i.e. α<α′), and the O_(C)-O_(R) line and theport reference line M1-M2 become close to parallel. Under the highpressure condition, at the first and second reference positions M1, M2at which the suction/discharge are switched, the O_(C)-O_(R) linebecomes close to the port reference line M1-M2. Consequently, adischarge amount fluctuation at the switch of the suction/dischargebecomes small, thereby stabilizing the discharge.

Effect of the Embodiment 1

A variable capacity vane pump comprises the pump body 10; the drivingshaft 2 rotatably supported by the pump body 10; the rotor 3 provided inthe pump body 10 and rotatably driven by the driving shaft 2; aplurality of vanes 32 radially extendably installed in their respectiveslots 31 that are arranged in a circumferential direction in the rotor3; the cam ring 4 rockably provided on the supporting surface N in thepump body 10 and forming a plurality of pump chambers B at the innercircumference 41 side of the cam ring 4 in cooperation with the rotor 3and the vanes 32; the side plate 6 and the second housing 12 provided atboth sides in the x-axis direction of the cam ring 4; the inlet port 62;121 provided at least one of the side plate 6 and the second housing 12and opening to a section of the pump chamber where a volume of the pumpchamber increases; the outlet port 63; 122 provided at least one of theside plate 6 and the second housing 12 and opening to a section of thepump chamber where the volume of the pump chamber decreases; and theseal member 50 provided at an outer circumference side of the cam ring 4and defining the first hydraulic pressure chamber A1 located at a sidewhere the pump discharge amount increases and the second hydraulicpressure chamber A2 located at a side where the pump discharge amountdecreases in the space (the hydraulic pressure chamber A) outside theouter circumference of the cam ring 4, and the center O_(C) of the camring 4 is offset to the inlet port 62; 121 side (the positive directionside of the z-axis) from the center O_(R) in the no-load state of thedriving shaft 2.

With this, at the switch of the suction/discharge under the highpressure condition, the discharge amount fluctuation becomes small, andthe decrease in the pump efficiency and the oscillation can besuppressed with the stable discharge.

The space between the adjacent vanes 32 is 1 pitch, and the center O_(C)of the cam ring 4 is offset to the inlet port 62, 121 side from the portreference line M1-M2 that connects the half-pitch-advanced position fromthe end edges of the inlet ports 62, 121 in the rotation direction ofthe rotor 3 (i.e. in the counterclockwise direction in FIGS. 2 to 6) andthe half-pitch-advanced position from the end edges of the outlet ports63, 122 in the rotation direction of the rotor 3.

With this, the angle defined by the O_(C)-O_(R) line and the portreference line M1-M2 during the pump drive becomes smaller than that ofthe conventional art, and the O_(C)-O_(R) line and the port referenceline M1-M2 become close to parallel. And, at the first and secondreference positions M1, M2 at which the suction/discharge are switched,the O_(C)-O_(R) line becomes close to the port reference line M1-M2.Accordingly, the discharge amount fluctuation at the switch of thesuction/discharge becomes small and the discharge is stable, andtherefore the decrease in the pump efficiency and the oscillation can besuppressed.

In the following, a modification example of the embodiment 1 will bedescribed.

Embodiment 1-1

FIG. 7 is an example in which the definition of the port reference lineis changed. In the embodiment 1, the first and second referencepositions M1, M2 at which the suction/discharge are switched and thedriving shaft center O_(R) are positioned on the one straight line.However, in the embodiment 1-1, a case where these are not positioned onthe one straight line is shown.

The center O_(C) of the cam ring 4 is offset to the inlet port 62, 121side from a port reference line M1-M2 which connects the center O_(R) ofthe driving shaft 2 in the no-load state and the first referenceposition M1 that is the half-pitch-advanced position from the end edges62 a, 121 a of the inlet ports 62, 121 or the second reference positionM2 that is the half-pitch-advanced position from the end edges 63 a, 122a of the outlet ports 63, 122.

With this setting, the same working and effects as the embodiment 1 canbe obtained. In the embodiment 1-1, since an M1-O_(R)-M2 line is a bentline, an M1-O_(R) line or an M2-O_(R) line is the port reference line.By properly changing the definition of the port reference line accordingto the characteristic of the vane pump 1, an optimum dischargeperformance can be gained. Here, the M1-O_(R)-M2 line of the bent linecould be the port reference line as it is.

Embodiment 2

Embodiment 2 will be explained on the basis of FIGS. 8 and 9. The basicstructure of the embodiment 2 is the same as the embodiment 1. In theembodiment 1, the cam ring center O_(C) is only set on the positivedirection side of the z-axis as compared with the port reference lineM1-M2, and an angle of the supporting surface “N” supporting the camring 4 at the negative direction side of the z-axis is not limited.

In contrast to this, the embodiment 2 is different from the embodiment 1in that an angle γ of the supporting surface “N” is provided. However,the cam ring center O_(C) in the no-load state is set at the positivedirection side of the z-axis (the inlet port 62, 121 side) as comparedwith the port reference line M1-M2 (including the driving shaft centerO_(R)). This point is same as the embodiment 1.

FIG. 8 is a sectional view of the part of the vane pump 1 according tothe embodiment 2. FIG. 9 is a schematic diagram showing a relationshipbetween the port reference line M1-M2 and the O_(C)-O_(R) line. In theembodiment 2, the supporting surface “N” slopes in the positivedirection of the z-axis as the supporting surface “N” extends in thepositive direction of the y-axis, and the angle γ with respect to theport reference line M1-M2 is set to 2°˜8° (in FIG. 8, M1′-M2′ is astraight line that passes through the pin 40 and is parallel to theM1-M2).

In addition, in FIG. 9, a thin alternate long and short dash line N-N isa straight line that is parallel to the supporting surface “N” of thecam ring 4. A thin alternate long and two short dashes line Y-Y is astraight line that is parallel to the y-axis. Therefore, the cam ring 4rocks along the N-N straight line. And as same as the supporting surface“N”, the N-N straight line is parallel to the ξ-axis, and its angle withrespect to the Y-Y straight line becomes γ.

The angle γ of the supporting surface “N” is designed normally by360°/(the number of vanes×4). The angle of the supporting surface “N” ofthe present vane pump 1 having 11 vanes is approximately 8° by thenormal design (see FIG. 10).

In FIG. 10, an inclination angle of the supporting surface “N” of thiscase is large, and the position in the positive direction of the z-axisof the cam ring 4 in the high speed state becomes high. With this, theposition of the cam ring center O_(C) is Widely offset from the drivingshaft center O_(R) in the positive direction of the z-axis.

Under the high pressure condition, since the driving shaft center O_(R)widely shifts to the positive direction side of the z-axis, an angle α1between a low speed high pressure O_(C)-O_(R) line that connects the camring center O_(C) and the driving shaft center O_(R) and the M1-M2 lineis not much changed. However, under the low pressure condition, withregard to an angle β1 between a high speed low pressure O_(C)-O_(R) lineand the M1-M2 line, since the shift amount of the driving shaft centerO_(R) is small, the positions of the center O_(C) and the center O_(R)are still separated in the z-axis direction (the embodiment 2, see FIG.9).

Because of this, although the inclination angle α of the O_(C)-O_(R)line with respect to the port reference line M1-M2 in the high pressurestate becomes small and becomes parallel, the inclination angle β in thelow pressure state becomes large. Thus, the first and second referencepositions M1, M2 at which the suction/discharge are switched and theO_(C)-O_(R) line are widely separated from each other, then the pumpdischarge becomes unstable.

As a consequence, in the embodiment 2, the angle γ of the supportingsurface “N” with respect to the port reference line M1-M2 is set to below, and its range is 2°˜8°. With this setting, the height in the z-axisdirection of the cam ring 4 becomes low, and the position in the z-axisdirection of the cam ring center O_(C) also becomes low (FIG. 9).

The cam ring center O_(C) in the no-load state is set on the positivedirection side of the z-axis as compared with the port reference lineM1-M2, and the cam ring center O_(C) becomes closer to the portreference line M1-M2 by an amount equivalent to the low setting of theangle γ of the supporting surface “N”.

Therefore, even in a case where the pump outlet pressure is low and thedriving shaft center O_(R) does not much shift to the positive directionside of the z-axis, since the cam ring center O_(C) is previouslypositioned close to the port reference line M1-M2, the positions in thez-axis direction of the center O_(C) and the center O_(R) are not widelyseparated from each other, and the inclination angle β1 of theO_(C)-O_(R) line with respect to the port reference line M1-M2 in thelow pressure state in the embodiment 2 becomes smaller than the lowpressure inclination angle β in the embodiment 1 (β1<β).

With this, even at the low pressure where the z-axis positive directionshift amount of the driving shaft center O_(R) is small, the O_(C)-O_(R)line becomes close to the first and second reference positions M1, M2 atwhich the suction/discharge are switched, and the pump discharge amountat the low pressure becomes stable.

As previously mentioned, the cam ring center O_(C) in the no-load stateis set at the positive direction side of the z-axis (the inlet port 62,121 side) as compared with the port reference line M1-M2 (including thedriving shaft center O_(R)), and this point is same as the embodiment 1.Thus, also at the high pressure, the inclination angle α1 of theO_(C)-O_(R) line with respect to the port reference line M1-M2 becomessmall, and the stability of the pump discharge amount at the highpressure is maintained.

Further, since the inlet pressure is supplied into the second hydraulicpressure chamber A2, the supporting force of the cam ring 4 by thesecond hydraulic pressure chamber A2 internal pressure cannot besufficiently obtained. The cam ring 4 is then likely to tilt to thesecond hydraulic pressure chamber A2 side. However, by limiting theangle of the supporting surface “N” within the range of 2°˜8°, the tiltof the cam ring 4 is prevented more effectively.

Effect of the Embodiment 2

In the embodiment 2, the range of the angle γ of the supporting surface“N” with respect to the port reference line M1-M2 is set to 2°˜8°. Withthis, even at the low pressure where the z-axis positive direction shiftamount of the driving shaft center O_(R) is small, it is possible tostabilize the pump discharge amount.

Although the invention has been described above by reference to certainembodiment of the invention, the invention is not limited to theembodiment described above. Further, design changes orengineering-change based on the embodiment are also included in theinvention.

The invention claimed is:
 1. A variable capacity vane pump comprising: apump body; a driving shaft rotatably supported by the pump body; a rotorprovided in the pump body and rotatably driven by the driving shaft; aplurality of vanes radially extendably installed in their respectiveslots that are arranged in a circumferential direction in the rotor; acam ring rockably provided on a supporting surface in the pump body andforming a plurality of pump chambers at an inner circumference side ofthe cam ring in cooperation with the rotor and the vanes, aneccentricity amount of the cam ring with respect to the rotor beingchanged by rotating of the cam ring on the supporting surface; first andsecond members provided at both sides in an axial direction of the camring; an inlet port provided at least at one of the first and secondmembers and opening to a suction section of the pump chamber where avolume of the pump chamber increases; an outlet port provided at leastat one of the first and second members and opening to a dischargesection of the pump chamber where the volume of the pump chamberdecreases; and a seal member provided at an outer circumference side ofthe cam ring and defining a first hydraulic pressure chamber located ata side where a pump discharge amount increases and a second hydraulicpressure chamber located at a side where the pump discharge amountdecreases in a space outside the outer circumference of the cam ring,wherein a center of the cam ring is provided (i) so as to be positionedat an inlet port side with respect to a center of the driving shaft in ano-load state in which a pressure difference between the suction sectionand the discharge section does not act on the driving shaft and therotor, and (ii) so as to be positioned at an outlet port side withrespect to the center of the driving shaft in a state in which thedriving shaft is elastically deformed to the inlet port side by theaction of the pressure difference on the driving shaft.
 2. The variablecapacity vane pump as claimed in claim 1, wherein the second hydraulicpressure chamber is supplied with at least an inlet pressure.
 3. Thevariable capacity vane pump as claimed in claim 1, wherein a line onwhich suction/discharge of the pump chamber are switched is defined as aport reference line, and the supporting surface is provided so that thesupporting surface gradually separates from the port reference line in adirection from the second hydraulic pressure chamber to the firsthydraulic pressure chamber.
 4. The variable capacity vane pump asclaimed in claim 1, wherein a range of an angle between the supportingsurface and the port reference line is 2°˜8°.